Process for production of an alcohol

ABSTRACT

A process for the production of alcohol, by hydrogenation of an aldehyde over a copper and zinc-containing catalyst includes the step of treating the reduced catalyst with a sulphur compound. The process reduces the hydrogenation of olefin contained in the aldehyde feed compared with a process using an untreated catalyst.

The present invention concerns selective hydrogenation processes andcatalysts for use in such processes. In particular the inventionconcerns selective hydrogenation of aldehyde groups to alcohols in thepresence of compounds containing olefin groups.

In the well-known processes for the production of alcohols by theso-called oxo process, an olefin is converted to an aldehyde byhydroformylation with carbon monoxide and hydrogen in the presence of acatalyst, which is typically a cobalt or a rhodium-based catalyst. Thealdehyde is then hydrogenated over a copper-containing catalyst to givean alcohol which is purified by distillation. This process is oftendescribed as a two-stage oxo process because hydroformylation andhydrogenation are carried out in separate process stages. Thehydroformylation product typically contains some unreacted olefin whichmay be removed from the process stream, normally by distillation, eitherbefore the hydrogenation or afterwards. The unreacted olefin may bereturned to the hydroformylation stage either as a continuous recycle,or, more commonly and efficiently, as a separate feed stream on acampaign basis, i.e. as a discontinuous recycle. The oxo-process isdescribed in various texts, for example in the Kirk-Othmer Encyclopaediaof Chemical Technology (John Wiley) 4^(th) Edn (1991), Vol1, p. 903-908.

The reaction product from the hydroformylation step contains typically80% aldehyde, the remainder being mainly unconverted olefin. When theunreacted olefin is not separated until after the hydrogenation of thealdehyde hydroformylation product, it is possible for the olefin to behydrogenated to saturated paraffin products, which are of relatively lowvalue. It is economically desirable to minimise the hydrogenation ofolefin so that it can be separated and recycled to hydroformylation forconversion to additional aldehyde. For this reason it is preferred touse a hydrogenation catalyst which is selective for the hydrogenation ofthe aldehyde group but which does not catalyse to a significant extentthe hydrogenation of the C═C double bond in the olefin materials.Catalysts based on copper with chromium and/or zinc have been describedfor this process, as for example in U.S. Pat. No. 2,549,416 in which theuse of such catalysts is described in detail.

U.S. Pat. No. 4,052,467 describes a process for the reduction ofoxo-aldehydes to alcohols over a Cu/ZnO containing catalyst in which thefeed contains a high concentration of thiophene (e.g. 500-2000 ppm) oranother ring-type sulphur compound. The reaction conditions arespecified to be in the range of temperature 450-550 degrees F. and apressure of 800-1200 psig with a LHSV in the range 1.0-1.5 to ensurethat the ring-type sulphur compounds in the feed do not decompose tosulphur or sulphur compounds which deleteriously affect the life of thecatalyst. According to the invention, we provide a process for theproduction of an alcohol by the hydrogenation of a feed streamcontaining at least one aliphatic aldehyde compound and an olefin over acatalyst comprising a copper compound and a zinc compound, andoptionally a catalyst support, comprising the step of treating saidcatalyst with an organic sulphur compound.

According to a second aspect of the invention, we provide a process forthe production of an alcohol, comprising the steps of:

-   (a) reacting an olefin feed with hydrogen and carbon monoxide in a    hydroformylation reactor in the presence of a suitable    hydroformylation catalyst to form a hydroformylation product stream    comprising an aldehyde and unreacted olefin,-   (b) optionally treating said hydroformylation product stream to    separate the catalyst from the remainder of the hydroformylation    product stream,-   (c) vaporising said hydroformylation product stream and feeding the    vapour together with a source of hydrogen to a hydrogenation reactor    containing a bed of a solid hydrogenation catalyst comprising a    copper compound and a zinc compound, to form a hydrogenation product    stream comprising an alcohol and unreacted olefin,-   (d) separating said hydrogenation product stream into at least an    alcohols stream and a stream containing said unreacted olefin,    characterised in that the hydrogenation catalyst is treated with an    organic sulphur compound before or during step (c).

We have found that the conversion of olefin to paraffin can besignificantly reduced, without significantly changing the conversion ofaldehyde to alcohol, by treating the hydrogenation catalyst with anorganic sulphur compound. The unreacted olefin is normally recycled tothe hydroformylation step either directly or, more preferably as aseparate feed stream. If fed as a discrete recycle stream, the olefinwhich is separated from the hydrogenation product stream is preferablystored and then fed to the hydroformylation reactor as a distinctcampaign so that the process conditions in the hydroformylation reactormay be optimised for the olefins contained in the recycle stream. Wehave also found that the conversion of aldehyde and product alcohol toalkane species in the hydrogenation reaction, e.g. by hydrogenolysis ofthe alcohol, can be significantly reduced using the process of thepresent invention, i.e. the selectivity of the catalyst to alcoholproduction is increased.

The treatment of the catalyst with an organic sulphur compound may bedone either prior to or during the feeding of the aldehyde-containingfeed stream to the catalyst. The sulphur compound can be added to theolefin feed before carrying out the hydroformylation in which case it isessential that the sulphur compound does not react under the conditionsof hydroformylation, in particular it must not be a poison for thehydroformylation catalyst. Alternatively and preferably, the sulphurcompound may be added to the crude aldehyde before it is fed to thehydrogenation reactor. It is preferred to treat the catalyst on-line,i.e. in situ in the hydrogenation reactor during the reduction of thecatalyst with hydrogen or after the catalyst has been reduced.

Thiophene is an example of a suitable compound as it has a high sulphurcontent and it is an easily handled liquid. The sulphur compound ispreferably fed to the catalyst as a vapour, optionally in the presenceof a diluent which may be an inert compound (e.g. nitrogen), hydrogen orthe aldehyde containing feed stream itself. Therefore preferred sulphurcompounds are vaporisable under suitable conditions, preferably underthe conditions at which the hydrogenation reaction is carried out. Otherthiophene compounds such as benzothiophene or a thiol (a mercaptan),e.g. alkyl thiols such as 1-butanethiol, may also be suitable. It ispreferred to use a sulphur compound which is conveniently stored andsupplied on the hydrogenation plant. Thiophene, being a liquid underambient conditions, is therefore particularly convenient to use in theprocess of the invention. Other sulphur compounds such as hydrogensulphide may, however, be effective.

The sulphur treatment is preferably carried out on a freshly reducedcatalyst by adding the sulphur compound to the hydrogenation feed overthe first 1 to 10 days on line at a concentration equivalent to lessthan about 150 ppm by weight S, e.g. 5-150 ppm, (preferably less than100 ppm S, e.g. from 5 to 100 ppm) based on feed. The quantity ofsulphur compound required is equivalent to 0.2 to 10 kg of sulphur pertonne of catalyst, preferably from 1 to 5 kg of sulphur per tonne ofcatalyst. In practice it is desirable to adjust the amount of sulphurcompound added by analysing the product stream. Therefore in preferredoperation, the sulphur compound is added to the feed stream and thecomposition of the product stream is monitored to determine that theolefin hydrogenation has reduced to a suitable level. If, after the feedof sulphur compound has ceased, the olefin hydrogenation has increasedthen it may be desirable to treat the catalyst with a further quantityof the sulphur compound. Different feeds, catalyst types and operatingconditions may affect the amount of sulphur compound required and, inpractice, the skilled person will optimise the treatment to suit theconditions and materials in use. If too much sulphur is added, thecatalyst activity may decline resulting in an increase in unconvertedaldehyde.

The aldehyde and olefin are typically the products of a hydroformylationreaction operated as part of a production process for oxo-alcohols. Thusthe feeds may vary widely from C3 to C20 olefins and above and theircorresponding Cn+1 aldehydes. Normally the olefin is a C3 to about C15compound or mixture of compounds and the aldehyde is C4 to about C16.

The olefin feeds may have terminal or internal unsaturation and may belinear or branched. Often, the olefin feed is a mixture of isomericcompounds produced as a fraction from a processed petroleum stream, forexample a mixed heptene or nonene fraction. Another commercially usefulfeed is made by dimerising a lower olefin feed, e.g. an octene feedproduced by dimerisation of a C4 olefin stream. Some oxo-processesincorporate an aldol condensation step in order to double the chainlength of the product aldehyde, for example to make 2-ethylhexenal froma propylene feed, so the feed composition suitable for the inventionincorporates such mixtures of olefin and aldehyde condensation product.An example of a suitable olefin is a C9 (nonenes) mixture. This isconverted by hydroformylation into a C10 aldehyde which is hydrogenatedto give the corresponding C10 alcohol (isodecanol).

The hydrogenation catalyst is normally supplied as pellets containing areducible form of a copper compound such as copper oxide and zinc oxide.The catalyst may, optionally, also include a support material and/orpromoter compounds. The catalyst support, if present is commonly aluminaalthough other suitable catalyst supports may be used. Various promotershave been proposed for copper oxide/zinc oxide catalysts and theseinclude alkali metal compounds, especially potassium or sodium, alkalineearth metals, e.g. magnesium, transition metal compounds, e.g.manganese, molybdenum, vanadium or zirconium or other metals such ascerium. Normally the promoter metal is present in the form of an oxide.Such promoters are known in the art. The copper compound is at leastpartially reduced to copper before the catalyst is brought on line.Suitable such catalysts are well known in the art and typically containCuO and ZnO at weight ratios of from about 4:1 to 1:4, especially 2:1 to1:3 (CuO:ZnO). As examples, suitable commercially available catalystsinclude PRICAT™ CZ 29/2, and PRICAT™ CZ 40/18, both available fromJohnson Matthey Catalysts.

The conditions for the hydrogenation reaction may vary between about 20barg and about 400 bar g. Typical aldehyde hydrogenation conditions areabout 230 bar pressure and from 240 to 280° C., more preferably fromabout 245 to 270° C. at a liquid feed rate of 1.25 m³/hour of aldehydeper te of catalyst and a hydrogen rate of 3,000 to 10,000 m³/h ofhydrogen per m³/hour of liquid (the hydrogen volume is that measured at20° C. and atmospheric pressure).

If no treatment is carried out, a freshly reduced catalyst may convertup to 80% of the olefin in the crude aldehyde to paraffin. Aftertreatment with a sulphur compound, the olefin conversion may be reducedto less than 30%, and often to less than 10%, so that more olefin isavailable to be recycled or otherwise recovered, leading to morefavourable process economics.

The following examples are for illustration only.

Example 1

A charge (16 tonne) of PRICAT™ CZ 29/2 CuO/ZnO catalyst available fromJohnson Matthey Catalysts, was reduced to the active form by treatmentwith a low concentration of hydrogen in nitrogen, initially at 190° C.and a pressure of 50 barg increasing to 260° C. and 100 barg as thereduction neared completion.

A mixed C9 olefin (nonenes) stream was hydroformylated to give a mixturecontaining C10 aldehyde, unconverted nonenes and by-products includingnonanes and high boiling C20 compounds. The crude aldehyde washydrogenated to give a crude C10 alcohol (isodecanol) by passing it overthe reduced hydrogenation catalyst in the presence of hydrogen at250-270° C. and 235 barg. The liquid feed rate was 20 m³/hour and thehydrogen rate was 90 000 m³/hour, the rate for the latter beingexpressed as at 20° C. and atmospheric pressure.

Over the first six days on line a total of about 67 litres (15 gallons)of thiophene was added to the hydrogenation feed, equivalent to 1.7 kg Sper tonne of catalyst. Over the next 10 days the olefin converted toparaffin was equivalent to 25% of the olefin in the feed. The residualaldehyde content of the crude alcohol product was less than 0.5% byweight.

COMPARATIVE EXAMPLE 1A

A similar charge of catalyst, which was not treated with thiophene, gave60-80% conversion of olefin to paraffin after 6 to 16 days on line. Theresidual aldehyde content of the crude alcohol was again less than 0.5%by weight.

EXAMPLE 2

A laboratory scale hydrogenation of nonanal, which had been produced bythe hydroformylation of di-isobutene, was carried out using amicroreactor containing a 10 ml sample of PRICAT CZ 29/2 (35 wt % copperoxide/65 wt % zinc oxide) catalyst. Nonanal consists predominantly(about 90% by weight) of a single isomer, which is3,5,5-trimethylhexanal.

The catalyst was reduced in the micro reactor at atmospheric pressureand 250° C. In a hydrogen-containing nitrogen stream flowing at 1 l/hr.the concentration of hydrogen in the gas stream was increased from 5% to100% over a period of about 10 hours. The reactor was then brought up tooperating pressure (200 barg) using neat hydrogen. The reactor was thenoperated at 300° C. at a gas:oil ratio of 7923:1, using the nonanal feedat a liquid feed rate of 15-20 ml/hour to show the performance of thecatalyst before treatment with the sulphur compound. The gas:oil ratiois the hydrogen flow rate ({overscore (R)}m³/hr, i.e. measured at 20° C.and 1 atmosphere) divided by the liquid feed rate (m³/hr). 0.2 ml ofthiophene was then added to the feed vessel contents (1.9 litres) andthe reactor was run continuously under the same conditions until thefeed had been consumed (7 days). Subsequently the reactor was run usingaldehyde feed containing no thiophene. The feed and product streams wereanalysed using temperature-programmed capillary gas chromatography.Table 1 shows the concentration of the major components in the feedstream and in the product stream over the course of the reaction.

The abbreviations used in the table are:

244 tmp: 2,4,4-trimethyl pentane

224 tmh: 2,2,4-trimethyl hexane

aldehyde: 3,5,5-trimethylhexanal

alcohol: 3,5,5-trimethylhexanol

heavies: heavy end products including dimer (C18) ester, dimer alcohol,dimer ether, trimers and other high boiling by products. TABLE 1 Day244tmp 224tmh Aldehyde Alcohol Heavies (Feed) 2.4 0.1 85.4 8.5 0.58 03.3 16.2 0.1 75.9 4.66 1 3.6 9.1 0.1 81.7 7.25 2 3.2 2.7 0.2 89.8 6.91 33.4 1.8 0.4 89.8 6.85 4 3.0 1.7 0.4 90.2 7.07 5 2.6 2.3 0.3 90.1 7.5 62.9 2.6 0.3 89.9 6.92 7 2.5 2.6 0.3 90.1 7.21 8 2.7 2.7 0.3 89.9 7 9 2.22.3 0.3 92.3 4.38 10 2.7 2.5 0.3 91.8 3.78 11 2.9 2.7 0.3 90.3 5.03

There is very little unhydroformylated olefin in the crude aldehydeproduct used in this example. The concentration of 2,4,4-trimethylpentane, which would be the product of hydrogenating di-isobutene isrelatively low and constant. However, the concentration of2,2,4-trimethyl hexane, which is at a very low level in the feed risesto over 16% when the hydrogenation takes place over un-treated catalyst.2,2,4-trimethyl hexane is present as a product of the hydrogenolysis ofthe product alcohol. It is very noticeable that during and aftertreatment with thiophene, the concentration of 2,2,4-trimethyl hexanefalls to about 2.5% with a corresponding increase in the concentrationof desired product alcohol in the product stream.

1. A process for the production of an alcohol by the hydrogenation of analiphatic aldehyde over a catalyst comprising a copper compound, and azinc compound comprising the step of treating said catalyst with anorganic sulphur compound.
 2. A process according to claim 1, whereinsaid aliphatic aldehyde is present in a feed stream containing anolefin.
 3. A process according to claim 2, wherein said feed stream isthe product of a hydroformylation reaction.
 4. A process according toclaim 1, wherein said organic sulphur compound comprises thiophene.
 5. Aprocess according to claim 1 wherein said organic sulphur compound ispresent at a concentration of from 5 ppm to 150 ppm by weight of sulphurin a feed stream containing said aldehyde based upon the total mass offeed.
 6. A process for the production of an alcohol, comprising thesteps of: (a) reducing a catalyst bed provided within a reactor with ahydrogen-containing gas stream; (b) feeding to the bed of said reducedcatalyst a gaseous feed stream comprising an aldehyde, a sulphurcompound, and hydrogen for a period of time sufficient to provide from0.2 to 10 kg of sulphur (S) per ton of catalyst wherein a concentrationof said sulphur compound in said feed stream is less than 150 ppm; and(c) subsequently feeding to said catalyst bed a feed stream containingno sulphur compound.
 7. A process for the production of an alcohol,comprising the steps of: (a) reacting an olefin feed with hydrogen andcarbon monoxide in a hydroformylation reactor in the presence of asuitable hydroformylation catalyst to form a hydroformylation productstream comprising an aldehyde and unreacted olefin; (b) vaporising saidhydroformylation product stream and feeding the vapour together with astream of a hydrogen-containing gas to a hydrogenation reactorcontaining a bed of a solid hydrogenation catalyst comprising a coppercompound and a zinc compound, to form a hydrogenation product streamcomprising at least an alcohol and said unreacted olefin; and (c)separating said hydrogenation product stream into at least an alcoholstream and a stream containing said unreacted olefin, wherein thehydrogenation catalyst is treated with an organic sulphur compoundbefore or during step (b).
 8. A process according to claim 1, whereinthe catalyst further comprises at least one of a catalyst support and apromoter compound.
 9. A process according to claim 7 further comprisingthe step of treating said hydroformylation product stream of step (a) toseparate the catalyst from the remainder of the hydroformylation productstream.